The present invention relates to a power supply apparatus for equipment, such as an arc welder, an arc cutter, a plasma arc welder, a plasma arc cutter, an electric charger and a noble metal plating apparatus.
Usually, this type of power supply apparatus converts commercial AC power into DC power by means of an AC-DC converter including, for example, a rectifier and a smoothing circuit. The DC power is then converted to high-frequency power by means of an inverter, and the high-frequency power from the inverter is voltage-transformed by a high-frequency transformer. The voltage-transformed high-frequency power is then converted back to DC power by a rectifier and a smoothing circuit, and the resulting DC power is applied to, for example, an arc welder.
The above-described arrangement requires no large voltage-transformer or choke coils, and, therefore, the power supply apparatus can be small in size and light in weight.
Japanese Unexamined Patent Publication No. HEI 8-140349 published on May 31, 1996 discloses a technique for further reducing the size and weight of power supply apparatuses of the above-described type. A power supply apparatus according to the disclosure in this Japanese unexamined patent publication includes a housing in which a power supply circuit is housed. The housing is formed by a front panel, a rear panel spaced from the front panel, and left and right side covers spaced from each other, which altogether define a space within the housing. The panels and covers are made of plastics for reducing the weight. Further, the left and right side covers are of the same shape so that the number of moldings required for fabricating the covers can be reduced. The abutment lines along which the top and bottom edges of the left and right side covers abut against each other for forming the housing together with the front and rear panels lie in the plain in which the vertical center lines extending through the front and rear panels lie.
A power supply apparatus with the above-described arrangement is often used outdoors, for example, an arc welder. In such a case, rain may enter into the interior of the housing through the abutment lines and drop on, for example, a printed circuit board on which a power supply circuit is arranged, to thereby cause failure of the power supply circuit.
Furthermore, because the housing is of plastics, the circuitry within the housing not only tends to be adversely affected by external radiation noise, but also tends to radiate noise. Such a power supply apparatus includes an inverter handling a high-frequency signal, as described above, and the inverter tends to radiate noise. When a plurality of arc welders powered from the above-described type of power supply apparatus are used simultaneously, noise radiated from the power supply apparatus of one arc welder may enter into the power supply apparatus of another arc welder to cause erroneous operation of the inverter of the latter power supply apparatus.
An objective of the present invention is to provide a power supply apparatus which is not only small in size and light in weight, but also provided with increased watertightness.
Another objective of the invention is to provide a power supply apparatus which is small in size and light in weight and tends to radiate little noise and tends to be little affected by noise from other equipment.